This invention relates generally to reversing nut constructions for use with diamond thread screws, and more particularly to devices of this type which are especially intended to undergo simple reciprocating movement along the length of the screw, with the reversing movements in the axial direction of travel of the nut being automatically accomplished.
In the past a number of mechanisms have been proposed and constructed for reversing the direction of travel of a nut carried by a diamond thread screw when the nut has reached one end of the screw thread. Such devices generally employed camming grooves having curved reversing edges at the opposite extremities of the screw. One prior construction employed an elongated groove follower which was contoured so as to closely follow the curvature of the grooves in the screw. The length of such a follower was in all cases sufficient to straddle the intersections of the grooves so that it would not jump from a left-hand to a right-hand groove or vice-versa. When these prior followers arrived at the ends of the screw, reversal of the nut could occur, because the reversing end grooves were considerably enlarged to enable the follower to swing from one groove to the oppositely directed groove.
The prior devices, however, had distinct disadvantages. The use of sliding follower members involved considerable friction between the members and the screw, due to the absence of any rolling parts. In addition, the reversing grooves had to undergo special machining in order to be wide enough to accommodate the swinging movement of the follower member as the nut reversed its axial direction of travel. Problems in obtaining proper geometry of such grooves, in order to provide smooth operation, were sometimes difficult to overcome, and the constructions which were proposed often proved too awkward to be physically realized.
Other devices employed merely a single fixed pin extending into the bore of the nut and engaging one of the grooves of the screw. Such devices were generally less than satisfactory in that no reliable drive means for insuring continuity of travel of the pin through the groove intersections was provided. Thus, there was always a danger that the pin might "jump" to the oppositely directed thread groove and thus reverse the nut's axial direction of travel prematurely.
U.S. Pat. No. 3,779,094 discloses a reversing nut construction for a diamond thread screw wherein the nut body incorporates a series of thread-engaging roller elements, one of which is fixed against axial or translational movement on the nut body, while others are capable of undergoing shifting movement respectively between oppositely disposed extreme positions. All of the rollers are carried by needle bearings, with ball-type thrust bearings and bowed spring washers for biasing the rollers into engagement with the screw threads. Those rollers which were axially shiftable were carried on slide blocks, respectively, which were movable in elongate slide grooves arranged parallel to the nut axis. In this later type of construction, virtually all friction which was encountered was of the rolling-type as opposed to the sliding type. As a result, very high efficiency and smooth operation were obtainable.
The present invention relates particularly to improvements in low-friction nut constructions from the standpoint of reduced cost and assembly time, together with greatly simplified structures whereby the manufacturing and assembly costs are less. One of the problems associated with the reversing nut device disclosed in the above identified patent is that the use of multiple needle bearings and thrust-type ball bearings tended to increase the overall cost of the device. In addition, the adjustment of such bearing assemblages tended to be both critical and time-consuming. Special machining was required on the screw in order to precisely form the grooves thereof in a way to accept the conical-shaped nose portions of the roller elements. Also, the slides on which the shiftable rollers were carried represented additional parts which had to be machined to close tolerances in order to insure smooth, trouble-free operation and performance.